Typically, the currently used incinerators comprise a hearth in the form of a chamber provided with a floor, or lower grate, below which is located an ash box and an outer wall made of heat-resistant material. A supply device opens from the exterior into the chamber in order to introduce waste material to be incinerated as the combustion takes place.
In order to reach a combustion as complete as possible, primary air is blown from below the grate and secondary air is blown above the burning stack to ensure a complete oxidation of the combustion gases and the solid residues which are carried by such gases.
In some cases, a portion of the secondary air is blown within the burning stack from the periphery of the combustion chamber still for the purpose of reaching a more complete combustion.
However, despite all precautions, it is noted that the rate of non-burnt gaseous or solid residues remains often substantially above the limits imposed by the regulations.